WO1988010462A1 - Procedure for controlling a radiation source and controllable radiation source - Google Patents
Procedure for controlling a radiation source and controllable radiation source Download PDFInfo
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- WO1988010462A1 WO1988010462A1 PCT/FI1988/000103 FI8800103W WO8810462A1 WO 1988010462 A1 WO1988010462 A1 WO 1988010462A1 FI 8800103 W FI8800103 W FI 8800103W WO 8810462 A1 WO8810462 A1 WO 8810462A1
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- radiation
- wavelength range
- led
- intensity
- radiation source
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- 230000005855 radiation Effects 0.000 title claims abstract description 135
- 238000000034 method Methods 0.000 title claims abstract description 18
- 230000003287 optical effect Effects 0.000 claims abstract description 28
- 238000001228 spectrum Methods 0.000 claims abstract description 22
- 230000001276 controlling effect Effects 0.000 claims abstract description 8
- 239000004065 semiconductor Substances 0.000 claims abstract description 8
- 230000001105 regulatory effect Effects 0.000 claims abstract description 4
- 230000003213 activating effect Effects 0.000 claims abstract description 3
- 238000003491 array Methods 0.000 claims abstract 2
- 238000005259 measurement Methods 0.000 claims description 17
- 230000005540 biological transmission Effects 0.000 claims description 8
- 239000000835 fiber Substances 0.000 claims description 5
- 238000012544 monitoring process Methods 0.000 claims description 2
- 238000013461 design Methods 0.000 description 4
- 238000010586 diagram Methods 0.000 description 2
- 206010052804 Drug tolerance Diseases 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 238000010276 construction Methods 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 230000017525 heat dissipation Effects 0.000 description 1
- 230000010354 integration Effects 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 238000004451 qualitative analysis Methods 0.000 description 1
- 238000004445 quantitative analysis Methods 0.000 description 1
- 230000003595 spectral effect Effects 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 230000001360 synchronised effect Effects 0.000 description 1
Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/255—Details, e.g. use of specially adapted sources, lighting or optical systems
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J1/00—Photometry, e.g. photographic exposure meter
- G01J1/02—Details
- G01J1/08—Arrangements of light sources specially adapted for photometry standard sources, also using luminescent or radioactive material
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J1/00—Photometry, e.g. photographic exposure meter
- G01J1/10—Photometry, e.g. photographic exposure meter by comparison with reference light or electric value provisionally void
- G01J1/20—Photometry, e.g. photographic exposure meter by comparison with reference light or electric value provisionally void intensity of the measured or reference value being varied to equalise their effects at the detectors, e.g. by varying incidence angle
- G01J1/28—Photometry, e.g. photographic exposure meter by comparison with reference light or electric value provisionally void intensity of the measured or reference value being varied to equalise their effects at the detectors, e.g. by varying incidence angle using variation of intensity or distance of source
- G01J1/30—Photometry, e.g. photographic exposure meter by comparison with reference light or electric value provisionally void intensity of the measured or reference value being varied to equalise their effects at the detectors, e.g. by varying incidence angle using variation of intensity or distance of source using electric radiation detectors
- G01J1/32—Photometry, e.g. photographic exposure meter by comparison with reference light or electric value provisionally void intensity of the measured or reference value being varied to equalise their effects at the detectors, e.g. by varying incidence angle using variation of intensity or distance of source using electric radiation detectors adapted for automatic variation of the measured or reference value
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
- G01J3/02—Details
- G01J3/0256—Compact construction
- G01J3/0259—Monolithic
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
- G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
- G01J3/02—Details
- G01J3/10—Arrangements of light sources specially adapted for spectrometry or colorimetry
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2201/00—Features of devices classified in G01N21/00
- G01N2201/06—Illumination; Optics
- G01N2201/062—LED's
- G01N2201/0621—Supply
Definitions
- the present invention concerns a procedure for controlling a radiation source, said radiation source being implemented with the aid of light-emitting diodes, or LEDs, of the radiation produced by them the desired wavelength range being separated and the intensity of this radiation range being controlled or kept constant.
- the present invention also concerns a controllable radiation source which has been composed of light-emittin diodes, or LEDs, and which comprises optical means for separating the desired wavelength range from the radiation produced by said LEDs and means for controlling the intensity of said wavelength range or keeping it constant.
- a radiation source of the kind described is used for instance in spectrometers and photometers. In frequent cases the radiation source is the most significant factor limiting the capacity of performance and usability of an instrument. In apparatus meant to be used in industrial conditions, as radiation source have usually been employed thermal radiators, such as sources based on an incandescent filament, for instance. Their problem is, however, poor optical efficiency and consequen high heat dissipation, as well as poor vibration toler ance, short service life and difficulty of modulation.
- LEDs are nearly ideal radiation sources for spectrometers in view of their narrow spectrum. However, high' price and poor stability are their problems. It is also a fact that the selection of standard wavelengths is scanty, particularly in the near IR range. LEDs enable, owing to their wider radiation spectrum, a considerably wider wavelength range to be covered', and they are also lower in price. The spectral radiance of LEDs is on the same order as that of most thermic radiation sources, or higher.
- the radiations spectrum of LEDs is mostly too wide to allow them to be used as such in spectrosc ⁇ pic measurements. Moreover, the shape of the radiation spectrum, the peak wavelength and the radiant power change powerfully with changing temperature and driving current, and with time.
- the measuring band is separated from the LEDs, usually, with the aid of separate filters, or the LED is used without filtering, in which case the resolution will also be poor.
- the variation of radiation intensity has most often been compensated for, either by mere electric compensation or by maintaining constant temperature of the LED, which has lead to a demanding and expensive mechanical design.
- the number of wavelengt bands in such pieces of apparatus is usually small (2 to 10).
- the object of the present invention is to eliminate, among others, the drawbacks mentioned above and to provide a novel procedure for controlling a radiation source, and a controllable radiation source. This is realized with the aid of the characteristic features of the invention stated un the claims hereto attached.
- a controllable radiation source can be realized which is simple as to its construction and contains no moving parts. Furthermore, the radiation source can be realized in a design with small external dimensions. Good wavelength resolution can be achieved in spite of small size.
- the wavelength resolution is determined, in the first place, be the size of the LED elements (typically only 300 ⁇ m by 300 ⁇ m) and by the angular dispersion and dimensions of the optics which disperse the radiation into a spectrum.
- the number of measuring channels in the spectrometer in which the procedure of the invention is applied may with ease be increased to be several dozen.
- the amount of required electronic control and driver apparatus is not necessarily dependent on the number of LEDs.
- the intensity of the wavelength bands is also stabilized.
- the creeping of the spectrum of the LEDs and of the total radiant power will then have no influence on the output intensity of the radiation source.
- the wavelengths of the radiation source may be electrically selected.
- the modulation frequency can be made very high if required (e.g. less than 1 ⁇ s per LED). It is possible in connection with the controllable radiation source of the in vention to use for detector a single-channel radiometer, in which advantageously one single detector element is used.
- the procedure, and the radiation source applying it can be used in the visible light and IR radiation ranges.
- the invention may be applied in the transmitter part of the spectrometer.
- a reliable and stable spectrometer, and one which is usable in field work, is obtained with the aid of such integration.
- Fig. 1 presents schematically a spectrometer in which the invention is applied
- Fig. 2 presents by way of example the radiation spectrum of a LED and the radiation spectrum achievable with the aid of the invention
- Fig. 3 presents in the form of a block diagram a LED row and its driver and control means
- Fig. 4 presents a radiation source according to the invention in which an optic fibre is utilized
- Fig. 5 presents schematically a reflection spectrometer in which the invention is applied
- Fig. 6 presents a radiation source row, Fig. 6B, by which a LED row, Fig. 6A, may be replaced.
- the radiation source is realized with a LED array composed of semiconductor chips, or LED elements, or equivalent. From the radiation of' the LED elements a wavelength range depending on the location of the LED element in said array is separated with an optical means dispersing radiation to a spectrum, and the intensity of this wavelength range, or output radiation, is controlled or maintained constant by observing its intensity and with its aid regulating the current passing through the respective LED element. The desired wavelength range may then be selected electrically by activating the respective element in the LED array.
- the radiation source 1 of the spectrometer has been composed of light-emitting, diodes, or LEDs.
- the radiation source 1 consists of a row of LEDs 2 which comprises a plurality of side-by- side LED semiconductor chips, or LED elements 21, 22,23, . . ., 26, which are all similar.
- the radiation source further comprises optical means for separating the desired wavelength range from the radiation produced by the LEDs, and means for maintaining the inten sity of the radiation in the wavelength range constant or on desired level.
- Said optical means consist of optical pieces of equipment, such as lenses, mirrors, gratings, slits and beam dividers, the radiation produced by the LEDs being collected and dispersed to a spectrum with the aid of said means, and the radiation of the desired wavelength range being directed on an output slit or equivalent.
- the optical means in the spectrometer of Fig. 1 include a radiation-collecting lens 3, a reflecting grating 5 dispersing the radiation to a spectrum, and a stop 6 presenting an output slit 6.
- radiation-collecting component e.g. a concave mirror, and in place of the reflection grating one may use a transmission grating or a prism. These components may also be combined by using, for instance, a focussing reflector or transmission grating.
- the controllable radiation source 1 of the invention further comprises optical means and a detector 7 for observing and/or measuring the intensity of the outgoing radiation.
- the optical means employed in the spectrometer of Fig. 1 consist of a beam divider 8.
- the radiation source also comprises a driver and control means 9, to which the detector 7 has been connected.
- the driver and control means 9 is connected to the LED row 2, to each of its elements 21, 22, ..., 26. With the aid of the driver and control means 9, the desired LED element is selected. Thus from the radiation produced by each LED element the desired wavelength range is directed on the output slit, this wavelength range depending on the location of the LED element 21, 22, ..., 26. From the radiation going out from the radiation source, part is separated with the aid of the optical means to go to the detector 7, the current flowing through the respective LED element and producing the radiation in question being regulated in accordance with the intensity data supplied by the detector and in such manner that the radiation intensity of that wavelength range, and thus the intensity of the output radiation, is constant.
- Fig. 1 the output radiation passing through the slot 6 is rendered parallel with a lens 10, whereafter it is directed on the object of measurement, 11.
- a receiver 12 After the object of measurement, in the direction of propagation of the radiation, follows a receiver 12, in which capacity in measurements made on diffuse objects advantageously serves a wide-area radiometer.
- the electric signal from the receiver 12 is amplified in an amplifier 13 and fed to a calculation unit 14, and it is possibly displayed on a display provided in conjunction therewith.
- the driver and control unit 9 of the radiation source 1 may possibly also be controlled.
- the radiation source 1 For reflection and/or transmission measurements, it is advantageous to devise at l east the radiation source 1 to be an integral unit. It can be suitably shielded against ambience, for instance enclosed in a hermetically sealed housing, for improved reliability.
- the circuitry of the driver and control means 9 is presented in block diagram form in Fig. 3.
- the LED elements are connected to a selector means 16, such as a decoder, and this is connected to the calculating unit 14.
- the desired LED element, for instance the element 23, and the desired wavelength range of the output radiation from the radiation source are selected with the aid of the selector means 16.
- Part of the radiation obtained from the LED elements is picked up with the aid of the optical means 8 and carried to the detector 7.
- the detector 7 is connected with the controller 9a.
- the current control circuit 15 is governed by the controller 9a with the aid of the signal from the detector 7, in such manner that the output signal of the detector has constantly the desired magnitude, whereby the intensity of the output radiation also maintains the desired level.
- Fig. 2 illustrates the spectrum of the output radiation obtained by the procedure of the invention.
- the ordinates represent the radiation intensity I and the abscissae, the wavelength
- the radiation spectrum of a standard LED has the shape of a broad bell curve, L, Fig. 2A.
- the spectra of the radiation coming from, a radiation source 1 according to the invention are narrow bands of desired height, or ranges, S, Figs 2B-2E, within the range delimited by the bell curve L.
- the spectrometer of Fig, 1 and the radiation source therein employed operate in principle as follows.
- the driver and control means 9 selects and activates in the LED row 2 the first LED element 21.
- the radiation of the LED element is collected with the lens 3 and sent as a parallel beam to the reflection grating 4.
- the lens 3 further produces of the radiation reflected by the grating a spectrum on the stop 5. That part of the radiation (wavelength range ⁇ 1 ) passes through the output slit 6 which is determined by the location of the LED element 21 in the row and by the locations and dimensioning of the other optical means 3,4,6. From the lens 10 a parallel output radiation is obtained, striking the object of measurement 11.
- part of the output radia tion is directed to strike the detector 7, and the signal representing the intensity that has been obtained is recorded with the driver and control means 9.
- the driver and control means adjusts the current going to the LED element 21 to have a value such that the signal obtained from the detector 7 rises to desired level, whereby the intensity of the output radiation also assumes the desired value, e.g. I o .
- the actual measurement takes place in the wavelength range ⁇ 1 (Fig. 2B) and the result is recorded in the calculating unit 14.
- the driver and control means 9 activates the LED element 22 and, after the output intensity has similarly been adjusted to required level, measurement takes place in the wavelength range ⁇ 2 (Fig. 2C).
- the driver and control means 9 activates all
- LED elements 21 ... 2N in succession and measurements are similarly carried out in the wavelength ranges ⁇ 3
- the calculating unit 14 is electrically synchronized with the driver and control means 9 so that all results of measurement that have been recorded can be coordinated with the correct wavelength ranges ⁇ 1 , . . . ⁇ 2 .
- the optical means for collecting the radiation from the LED rows, for dispersing it to a spectrum and for directing the desired wavelength range on the output slit 6, comprising a lens 3 and a reflection grating 4 or equivalent.
- said optical means comprise a beam divider cube 17 and on the surface thereof a focussing transmission grating 18.
- the detector 7 for monitoring the intensity of the output radiation has been disposed in conjunction with the beam divider cube 17.
- the dividing interface 17a of the beam divider cube reflects to the detector 7 part of the radiation going through the beam divider cube to the output slit.
- In the capacity of output slit serves an optic fibre connector 19 to which an optic fibre 31 has been connected.
- the radiation source 1 with its LED row 2 is enclosed in a suitable housing 32.
- Fig. 5 depicts a compact spectrometer intended for reflection measurements and comprising both the transmitter of the radiation source and the receiver.
- the radiation source 1 is equivalent in its design with the radiation source of Fig. 4, and the same reference numerals are employed to indicate equivalent components.
- a receiver 33 In front of the radiation source 1, in the direction of propagation of the radiation, a receiver 33 has been disposed. This receiver consists of a beam divider 34 and a receiver detector 12. The output radiation is carried put from the device through an aperture 35.
- the object of measurement 36 which is a reflecting surface, is placed in front of the radiation beam coming from the spectrometer.
- the radiation reflected from the object of measurement 36 returns through the aperture 35 to the beam divider 34 of the receiver 33, from the dividing interface 34a of which the major part of the radiation is reflected to the receiver detector 12 and is detected.
- Both the radiation source 1 and the receiver 33 have in this case been integrated to constitute a single unit, which may be provided with a hermetically sealed housing 36 if required. In this way the reflection spectrometer can be made into a device usable in the field.
- the radiation from the spectrometer can be directed to strike the object of measurement 36 without any separate output optics, as has been set forth in the foregoing, or by using e.g. a standard lens optic system or a fibreoptic component.
- the LED row may be replaced with another type of radia tion source row, as can be seen in Fig. 6.
- Fig. 6A presents, seen from the side, a LED row 2 comprising consecutively placed LED elements 21, 22, ..., 2N.
- the alternative radiation source row depicted in Fig. 6B comprises a number of LED elements or separate, encapsulated LEDs 21, 22, ..., 27, to each of them connecte an optic fibre 41, 42, ..., 47 by its first end 41a, 42a, ..., 47a.
- the other ends 41b, 42b, ..., 47b of the optic fibres are arranged in a configuration such as is desired.
- the ends of the optic fibres are then close together and are thus equivalent e.g. to the LED row presented in the foregoing.
Abstract
The present invention concerns a procedure for controlling a radiation source which has been implemented with the aid of light-emitting diodes, or LEDs, from the radiation produced by them being separated the desired wavelength range, of which the intensity is controlled or maintained constant. The radiation source is implemented by means of a LED row (2) formed of semiconductor chips, or LED elements, (21, 22, 23,..., 26), from the radiation of which is separated a wavelength range (DELTAlambda1, DELTAlambda2,...) depending on the location of the LED element in said arrays with an optical means dispersing the radiation to a spectrum, and the intensity of the radiation in this wavelength range, or of the output radiation, is controlled or maintained constant by observing the intensity thereof and regulating with its aid the current passing through the respective LED element. The wavelength ranges of the output radiation are selected electrically by activating a suitable LED element (21, 22, 23,..., 26) in the LED row (2).
Description
PROCEDURE FOR CONTROLLING A RADIATION SOURCE AND CONTROLLABLE RADIATION SOURCE
The present invention concerns a procedure for controlling a radiation source, said radiation source being implemented with the aid of light-emitting diodes, or LEDs, of the radiation produced by them the desired wavelength range being separated and the intensity of this radiation range being controlled or kept constant.
The present invention also concerns a controllable radiation source which has been composed of light-emittin diodes, or LEDs, and which comprises optical means for separating the desired wavelength range from the radiation produced by said LEDs and means for controlling the intensity of said wavelength range or keeping it constant.
A radiation source of the kind described is used for instance in spectrometers and photometers. In frequent cases the radiation source is the most significant factor limiting the capacity of performance and usability of an instrument. In apparatus meant to be used in industrial conditions, as radiation source have usually been employed thermal radiators, such as sources based on an incandescent filament, for instance. Their problem is, however, poor optical efficiency and consequen high heat dissipation, as well as poor vibration toler ance, short service life and difficulty of modulation.
In recent years the development of semiconductor technology has introduced on the market efficient lasers based on semiconductor junctions, and light-emitting diodes, or LEDs. They afford several advantages over traditional radiation sources: for instance, small size and low energy consumption, good reliability, long ser
vice life (even more than 10° hours), high operating speed, easy connection to optic fibres. Furthermore, they can be electrically modulated with ease. Semiconductor radiation sources are nowadays available for the wavelength range about 400 nm to over 10 μm; admittedly, though, for operation at room temperature only up to about 3200 nm. The said range is usable in quantitative and qualitative analysis of most substances.
Semiconductor lasers are nearly ideal radiation sources for spectrometers in view of their narrow spectrum. However, high' price and poor stability are their problems. It is also a fact that the selection of standard wavelengths is scanty, particularly in the near IR range. LEDs enable, owing to their wider radiation spectrum, a considerably wider wavelength range to be covered', and they are also lower in price. The spectral radiance of LEDs is on the same order as that of most thermic radiation sources, or higher.
The radiations spectrum of LEDs is mostly too wide to allow them to be used as such in spectroscαpic measurements. Moreover, the shape of the radiation spectrum, the peak wavelength and the radiant power change powerfully with changing temperature and driving current, and with time.
In spectrometer designs of prior art based on the use of LED sources, the measuring band is separated from the LEDs, usually, with the aid of separate filters, or the LED is used without filtering, in which case the resolution will also be poor. The variation of radiation intensity has most often been compensated for, either by mere electric compensation or by maintaining constant temperature of the LED, which has lead to a demanding and expensive mechanical design. Owing to the high price and difficult manipulation of the filters
(e.g. miniaturizing, cutting), the number of wavelengt bands in such pieces of apparatus is usually small (2 to 10).
The object of the present invention is to eliminate, among others, the drawbacks mentioned above and to provide a novel procedure for controlling a radiation source, and a controllable radiation source. This is realized with the aid of the characteristic features of the invention stated un the claims hereto attached.
With the aid of the invention the following advantages are gained, among others. On the basis of the procedure of the invention a controllable radiation source can be realized which is simple as to its construction and contains no moving parts. Furthermore, the radiation source can be realized in a design with small external dimensions. Good wavelength resolution can be achieved in spite of small size. The wavelength resolution is determined, in the first place, be the size of the LED elements (typically only 300 μm by 300 μm) and by the angular dispersion and dimensions of the optics which disperse the radiation into a spectrum. The number of measuring channels in the spectrometer in which the procedure of the invention is applied may with ease be increased to be several dozen. The amount of required electronic control and driver apparatus is not necessarily dependent on the number of LEDs. According to the procedure, the intensity of the wavelength bands is also stabilized. The creeping of the spectrum of the LEDs and of the total radiant power will then have no influence on the output intensity of the radiation source. According to the procedure, the wavelengths of the radiation source may be electrically selected. The modulation frequency can be made very high if required (e.g. less than 1 μs per LED). It is possible in connection with the controllable radiation source of the in
vention to use for detector a single-channel radiometer, in which advantageously one single detector element is used. The procedure, and the radiation source applying it, can be used in the visible light and IR radiation ranges.
The invention may be applied in the transmitter part of the spectrometer. In certain applications it is also possible to integrate the whole spectrometer to be one single component, which may be hermetically encapsulated. A reliable and stable spectrometer, and one which is usable in field work, is obtained with the aid of such integration.
Significant advantages are gainable with the aid of the procedure of the invention, and of the radiation source employing it, in reflection or transmission measurements on diffuse objects, compared with the multiple detector technique, which has become commonly used in recent years. In multiple element spectrometers the diffuse radiation has to be collected on small-sized detector elements through a narrow entrance slit, whereby high optical collection losses are incurred. In the controllable radiation source of the invention, the optical collection losses can be minimized by using for detector the single-channel radiometer mentioned above, which has a large-sized detector element and, at the same time, also a wide collection angle.
The invention is .described in detail in the following with the aid of the attached drawings; wherein:-
Fig. 1 presents schematically a spectrometer in which the invention is applied;
Fig. 2 presents by way of example the radiation spectrum of a LED and the radiation spectrum achievable
with the aid of the invention;
Fig. 3 presents in the form of a block diagram a LED row and its driver and control means;
Fig. 4 presents a radiation source according to the invention in which an optic fibre is utilized; and
Fig. 5 presents schematically a reflection spectrometer in which the invention is applied,
Fig. 6 presents a radiation source row, Fig. 6B, by which a LED row, Fig. 6A, may be replaced.
In the procedure of the invention the radiation source is realized with a LED array composed of semiconductor chips, or LED elements, or equivalent. From the radiation of' the LED elements a wavelength range depending on the location of the LED element in said array is separated with an optical means dispersing radiation to a spectrum, and the intensity of this wavelength range, or output radiation, is controlled or maintained constant by observing its intensity and with its aid regulating the current passing through the respective LED element. The desired wavelength range may then be selected electrically by activating the respective element in the LED array.
In the spectrometer of Fig. 1 the procedure of the invention is applied. The radiation source 1 of the spectrometer has been composed of light-emitting, diodes, or LEDs. Specifically, the radiation source 1 consists of a row of LEDs 2 which comprises a plurality of side-by- side LED semiconductor chips, or LED elements 21, 22,23, . . ., 26, which are all similar. The radiation source further comprises optical means for separating the desired wavelength range from the radiation produced by the LEDs, and means for maintaining the inten
sity of the radiation in the wavelength range constant or on desired level. Said optical means consist of optical pieces of equipment, such as lenses, mirrors, gratings, slits and beam dividers, the radiation produced by the LEDs being collected and dispersed to a spectrum with the aid of said means, and the radiation of the desired wavelength range being directed on an output slit or equivalent. The optical means in the spectrometer of Fig. 1 include a radiation-collecting lens 3, a reflecting grating 5 dispersing the radiation to a spectrum, and a stop 6 presenting an output slit 6. It is equally possible to use for radiation-collecting component e.g. a concave mirror, and in place of the reflection grating one may use a transmission grating or a prism. These components may also be combined by using, for instance, a focussing reflector or transmission grating.
The controllable radiation source 1 of the invention further comprises optical means and a detector 7 for observing and/or measuring the intensity of the outgoing radiation. The optical means employed in the spectrometer of Fig. 1 consist of a beam divider 8. The radiation source also comprises a driver and control means 9, to which the detector 7 has been connected.
The driver and control means 9 is connected to the LED row 2, to each of its elements 21, 22, ..., 26. With the aid of the driver and control means 9, the desired LED element is selected. Thus from the radiation produced by each LED element the desired wavelength range is directed on the output slit, this wavelength range depending on the location of the LED element 21, 22, ..., 26. From the radiation going out from the radiation source, part is separated with the aid of the optical means to go to the detector 7, the current flowing through the respective LED element and producing the radiation in question being regulated in accordance
with the intensity data supplied by the detector and in such manner that the radiation intensity of that wavelength range, and thus the intensity of the output radiation, is constant.
Also other optical means may further be attached to the radiation source 1. In Fig. 1, the output radiation passing through the slot 6 is rendered parallel with a lens 10, whereafter it is directed on the object of measurement, 11. After the object of measurement, in the direction of propagation of the radiation, follows a receiver 12, in which capacity in measurements made on diffuse objects advantageously serves a wide-area radiometer. The electric signal from the receiver 12 is amplified in an amplifier 13 and fed to a calculation unit 14, and it is possibly displayed on a display provided in conjunction therewith. With the calculating unit 14, or by controls on a panel provided in conjunction therewith, the driver and control unit 9 of the radiation source 1 may possibly also be controlled.
For reflection and/or transmission measurements, it is advantageous to devise at l east the radiation source 1 to be an integral unit. It can be suitably shielded against ambience, for instance enclosed in a hermetically sealed housing, for improved reliability.
The circuitry of the driver and control means 9 is presented in block diagram form in Fig. 3. The LED elements 21, 22, ..., 2(N-1), 2N (N = an integer 1, 2, 3, ...) has been connected over a current control circuit 15 to a voltage source 30. The LED elements are connected to a selector means 16, such as a decoder, and this is connected to the calculating unit 14. The desired LED element, for instance the element 23, and the desired wavelength range of the output radiation from the radiation source are selected with the aid of the
selector means 16. Part of the radiation obtained from the LED elements is picked up with the aid of the optical means 8 and carried to the detector 7. The detector 7 is connected with the controller 9a. The current control circuit 15 is governed by the controller 9a with the aid of the signal from the detector 7, in such manner that the output signal of the detector has constantly the desired magnitude, whereby the intensity of the output radiation also maintains the desired level.
Fig. 2 illustrates the spectrum of the output radiation obtained by the procedure of the invention. In the rectangular coordinates, the ordinates represent the radiation intensity I and the abscissae, the wavelength The radiation spectrum of a standard LED has the shape of a broad bell curve, L, Fig. 2A. The spectra of the radiation coming from, a radiation source 1 according to the invention are narrow bands of desired height, or ranges, S, Figs 2B-2E, within the range delimited by the bell curve L.
The spectrometer of Fig, 1 and the radiation source therein employed operate in principle as follows. The driver and control means 9 selects and activates in the LED row 2 the first LED element 21. The radiation of the LED element is collected with the lens 3 and sent as a parallel beam to the reflection grating 4. The lens 3 further produces of the radiation reflected by the grating a spectrum on the stop 5. That part of the radiation (wavelength range Δλ1 ) passes through the output slit 6 which is determined by the location of the LED element 21 in the row and by the locations and dimensioning of the other optical means 3,4,6. From the lens 10 a parallel output radiation is obtained, striking the object of measurement 11.
Through the optical means 8, part of the output radia
tion is directed to strike the detector 7, and the signal representing the intensity that has been obtained is recorded with the driver and control means 9. The driver and control means adjusts the current going to the LED element 21 to have a value such that the signal obtained from the detector 7 rises to desired level, whereby the intensity of the output radiation also assumes the desired value, e.g. Io. Hereafter the actual measurement takes place in the wavelength range Δλ1 (Fig. 2B) and the result is recorded in the calculating unit 14. Next, the driver and control means 9 activates the LED element 22 and, after the output intensity has similarly been adjusted to required level, measurement takes place in the wavelength range Δλ2 (Fig. 2C). The driver and control means 9 activates all
LED elements 21 ... 2N in succession and measurements are similarly carried out in the wavelength ranges Δλ3
..., Δλ4 (Fig, 2E), whereafter the driver and control means 9 activates again the LED element 21, and so on. The calculating unit 14 is electrically synchronized with the driver and control means 9 so that all results of measurement that have been recorded can be coordinated with the correct wavelength ranges Δλ1, . . . Δλ2.
In the foregoing in the spectrometer of Fig. 1 the optical means for collecting the radiation from the LED rows, for dispersing it to a spectrum and for directing the desired wavelength range on the output slit 6, comprising a lens 3 and a reflection grating 4 or equivalent. In the .radiation source of Fig. 4, said optical means comprise a beam divider cube 17 and on the surface thereof a focussing transmission grating 18. In this case the detector 7 for monitoring the intensity of the output radiation has been disposed in conjunction with the beam divider cube 17. The dividing interface 17a of the beam divider cube reflects to the detector 7 part of the radiation going through the beam
divider cube to the output slit. In the capacity of output slit serves an optic fibre connector 19 to which an optic fibre 31 has been connected. The radiation source 1 with its LED row 2 is enclosed in a suitable housing 32.
Fig. 5 depicts a compact spectrometer intended for reflection measurements and comprising both the transmitter of the radiation source and the receiver. The radiation source 1 is equivalent in its design with the radiation source of Fig. 4, and the same reference numerals are employed to indicate equivalent components. In front of the radiation source 1, in the direction of propagation of the radiation, a receiver 33 has been disposed. This receiver consists of a beam divider 34 and a receiver detector 12. The output radiation is carried put from the device through an aperture 35. The object of measurement 36, which is a reflecting surface, is placed in front of the radiation beam coming from the spectrometer. The radiation reflected from the object of measurement 36 returns through the aperture 35 to the beam divider 34 of the receiver 33, from the dividing interface 34a of which the major part of the radiation is reflected to the receiver detector 12 and is detected. Both the radiation source 1 and the receiver 33 have in this case been integrated to constitute a single unit, which may be provided with a hermetically sealed housing 36 if required. In this way the reflection spectrometer can be made into a device usable in the field. The radiation from the spectrometer can be directed to strike the object of measurement 36 without any separate output optics, as has been set forth in the foregoing, or by using e.g. a standard lens optic system or a fibreoptic component.
The LED row may be replaced with another type of radia
tion source row, as can be seen in Fig. 6. Fig. 6A presents, seen from the side, a LED row 2 comprising consecutively placed LED elements 21, 22, ..., 2N. The alternative radiation source row depicted in Fig. 6B comprises a number of LED elements or separate, encapsulated LEDs 21, 22, ..., 27, to each of them connecte an optic fibre 41, 42, ..., 47 by its first end 41a, 42a, ..., 47a. The other ends 41b, 42b, ..., 47b of the optic fibres are arranged in a configuration such as is desired. The ends of the optic fibres are then close together and are thus equivalent e.g. to the LED row presented in the foregoing.
It should be noted that although the invention has been presented in the foregoing in the first place only with the aid of one measuring apparatus, it is obvious that the procedure for controlling a radiation source, and the controlled radiation source, can be employed in numerous other applications as well in which a stable, or easy to control, radiation source is needed which produces radiation within a given wavelength range in a plurality of al ternatingly active, and if need be narrow, wavelength bands. Moreover, in the embodiment examples of the invention presented in the foregoing a LED row or equivalent is employed, but it is also possible to use in its stead a LED matrix or any other equivalent LED array.
Claims
1. A procedure for controlling a radiation source which has been implemented with the aid of light-emitting diodes, or LEDs, from the radiation produced by them being separated the desired wavelength range, of which the intensity is controlled or maintained constant, characterized in that the radiation source is implemented by means of a LED array (2) or equivalent (2') formed of LED elements (21, 22, 23, ..., 26), from the radiation of which is separated a wavelength range ( Δλ1, Δλ2, ...) depending on the location of the LED element in said arrays with an optical means dispersing the radiation to a spectrum, and the intensity (Io) of the radiation in this wavelength range, or of the output radiation, is controlled or maintained constant by observing the intensity thereof and regulating with its aid the current passing through the respective LED element.
2. Procedure according to claim 1, characterized in that the wavelength ranges (Δλ1, Δλ2, ...) of the output radiation are selected electrically by activating a suitable LED element (21, 22, 23, ..., 26) of the LED array (2,2').
3. A controllable radiation source (1) which is composed of light-emitting diodes, or LEDs, and which comprises optical means for separating the desired wavelength range from the radiation produced by the- LEDs and means for controlling or keeping constant the intensity of said wavelength range, characterized in that the radiation source consists of a LED array (2,2') which comprises a plurality of side-by-side LED semiconductor chips, or LED elements (21, 22, 23, ..., 26) or equivalent; the optical means consist of optical apparatus (3,4,6), with the aid of said apparatus the radiation produced by the LEDs being collected and the radiation dispersed to a spectrum and the desired wavelength range ( Δλ1, Δλ2, ...) of the spectrum being directed on an output slit (6) or equivalent; optical means (8) and a detector (7) for monitoring and/or measuring the intensity (Io) of the output radiation; and a driver and control means (9) by the aid of which from the radiation produced by each LED element is selected to the output slit (6) the desired wavelength range, which depends on the location of the LED element (21, 22, 23, ..., 26) in the LED array (2,2') and from which output radiation part is with the aid of optical means (8) separated to go to a detector (7) according to the intensity values from which the driver and control unit (9) regulates the current passing through the respective LED element so that the intensity (Io) of the radiation in said wavelength range and of the output radiation is maintained at desired height.
4. Means according to claim 3, characterized in that the LED elements (21, 22, 23, ..., 26) of the LED array (2,2') are connected together and connected with a current control circuit (15) and a selector means (16) with the aid of which the desired LED element (e.g. 23) and the desired wavelength range (Δλ3) of the output radiation of the radiation source are selected and which current control circuit (15) is governed by a controller (9a) with the aid of the signal from the detector (7) in such manner that the intensity (Io) of the output radiatiqneontinuously maintains the same height.
5. Means according to claim 3 or 4, characterized in that said optical means for collecting and dispersing to a spectrum the radiation produced by the LEDs and for directing the desired wavelength range on the output slit (6) comprise a focussing reflection or trans mission grating.
6. Means according to claim 3 or 4, characterized in that said optical means for collecting and dispersing to a spectrum the radiation produced by the LEDs and for directing the desired wavelength range on the output slit (6) and on the detector (7) comprise a beam divider cube (17) and on then surface thereof a transmission grating (18).
7. Means according to claim 6, characterized in that the detector (7) for observing the intensity of the output radiation has been disposed in conjunction with the beam divider cube (17) so that the beam divider cube also serves as an optical means associated with the detector.
8. Means according to any one of the preceding claims 3-7 for performing reflection and/or transmission measurement , characterized in that at least the radiation source (1) has been formed to be an integral unit (32).
9. Means according to any one of the preceding claims 3-7 for performing reflection measurements, characterized in that, the radiation source (1) and the receiver (33) have been integrated to constitute an integrated unit, which is advantageously provided with a hermetically sealed housing (37).
10. Means according to any one of the preceding claims 3-7, characterized in that the LED array (2') consists of a plurality of LED elements or separate encapsulated LEDs (21, 22, ..., 27,Fig. 6B) to each of which is connected an optic fibre (41, 42, ..., 47) by its first end (41a, 42a, ..., 47a) and the second ends (41b, 42b, ..., 47b) have been arranged in a desired configuration.
Priority Applications (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
DE3852176T DE3852176T2 (en) | 1987-06-25 | 1988-06-23 | METHOD FOR CONTROLLING A RADIATION SOURCE AND A REGULATABLE RADIATION SOURCE. |
EP88905853A EP0366696B1 (en) | 1987-06-25 | 1988-06-23 | Procedure for controlling a radiation source and controllable radiation source |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
FI872824A FI77736C (en) | 1987-06-25 | 1987-06-25 | FOERFARANDE FOER REGLERING AV STRAOLKAELLA OCH REGLERBAR STRAOLKAELLA. |
FI872824 | 1987-06-25 |
Publications (1)
Publication Number | Publication Date |
---|---|
WO1988010462A1 true WO1988010462A1 (en) | 1988-12-29 |
Family
ID=8524727
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/FI1988/000103 WO1988010462A1 (en) | 1987-06-25 | 1988-06-23 | Procedure for controlling a radiation source and controllable radiation source |
Country Status (5)
Country | Link |
---|---|
US (1) | US5029245A (en) |
EP (1) | EP0366696B1 (en) |
DE (1) | DE3852176T2 (en) |
FI (1) | FI77736C (en) |
WO (1) | WO1988010462A1 (en) |
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Also Published As
Publication number | Publication date |
---|---|
FI77736B (en) | 1988-12-30 |
DE3852176T2 (en) | 1995-06-22 |
EP0366696B1 (en) | 1994-11-23 |
US5029245A (en) | 1991-07-02 |
FI872824A0 (en) | 1987-06-25 |
EP0366696A1 (en) | 1990-05-09 |
FI77736C (en) | 1989-04-10 |
DE3852176D1 (en) | 1995-01-05 |
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